German wartime submarine (5)

I think it could be either:

Which length description are you looking for?:

1-4

u-boat

'german wartime submarine' is the definition.
(I've seen this before)

This is the entire clue.

(Other definitions for u-boat that I've seen before include "Submersible warship armed with torpedoes" , "About (anag)" , "Submersible warship of WWII" , "German wartime submarine" , "German WW 2 sub" .)

I've seen this clue in The Times.

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